Method and system for protecting a wireless power transfer system

ABSTRACT

A wireless power transfer system is disclosed. The wireless power transfer system includes a first converting unit configured to convert a first DC voltage of an input power to a first AC voltage. Further, the wireless power transfer system includes a contactless power transfer unit configured to receive the input power having the first AC voltage from the first converting unit and transmit the input power. Also, the wireless power transfer system includes a second converting unit configured to receive the input power from the contactless power transfer unit and convert the first AC voltage of the input power to a second DC voltage. Furthermore, the wireless power transfer system includes a switching unit configured to regulate the second DC voltage across the electric load if the second DC voltage across the electric load is greater than a voltage reference value.

RELATED APPLICATIONS

This application is a Continuation of and claims the priority benefit ofU.S. application Ser. No. 15/420,139 filed Jan. 31, 2017 which claimsthe priority benefit of India Application No. 201641003929 filed Feb. 3,2016.

BACKGROUND

Embodiments of the present invention relate generally to wireless powertransfer systems and more particularly to a system and method forprotecting a wireless power transfer system.

In one or more industries, an electric vehicle or a hybrid vehicleincludes one or more batteries that supply electrical power to drive thevehicle. In one example, the batteries supply energy to an electricmotor to drive a shaft in the vehicle, which in turn drives the vehicle.The batteries are used for supplying the power and hence may be drainedand need to be charged from an external power source.

In general, power transfer systems are widely used to transfer powerfrom a power source to one or more electric loads, such as for example,the batteries in the vehicle. Typically, the power transfer systems maybe contact based power transfer systems or contactless power transfersystems. In the contact based power transfer systems, components, suchas plug, socket connectors, and wires are physically coupled to thebatteries for charging the batteries. However, due to environmentalimpact, such connectors and wires may be damaged or corroded. Also, highcurrents and voltages are used for charging the batteries. Hence,establishing a physical connection between the power source and thebatteries in the vehicle may involve cumbersome safety measures. Also,this power transfer system may become bulkier and heavier compared tothe contactless power transfer system.

In the contactless power transfer systems, power converters are used toconvert an input power to a transferrable power, which is furthertransmitted to the electric load, such as the batteries in the vehicle.The power converter includes switches which are operated at a particularswitching frequency to convert the input power to the transferrablepower. Typically, depending upon the load, the switching frequency ofthe power converter is changed to regulate or control an output voltageof the power transfer system. However, if the electric load isdisconnected or varied, the output voltage of the power transfer systemmay attain a very high value in a very short time period. Such a suddenincrease in the output voltage may lead to failure of operation and mayalso damage one or more components in the power transfer system.

Therefore, there is a need for an improved system and method forprotecting the power transfer system.

BRIEF DESCRIPTION

In accordance with one embodiment of the present invention, a wirelesspower transfer system is disclosed. The wireless power transfer systemincludes a first converting unit configured to convert a first DCvoltage of an input power to a first AC voltage. Further, the wirelesspower transfer system includes a contactless power transfer unitcommunicatively coupled to the first converting unit and configured toreceive the input power having the first AC voltage from the firstconverting unit and transmit the input power. Also, the wireless powertransfer system includes a second converting unit communicativelycoupled to the contactless power transfer unit and configured to receivethe input power from the contactless power transfer unit and convert thefirst AC voltage of the input power to a second DC voltage. The inputpower having the second DC voltage is transmitted to an electric load.Furthermore, the wireless power transfer system includes a switchingunit coupled to the contactless power transfer unit and the secondconverting unit and configured to regulate the second DC voltage acrossthe electric load if the second DC voltage across the electric load isgreater than a voltage reference value.

In accordance with another embodiment of the present invention, aswitching unit for protecting a wireless power transfer system isdisclosed. The switching unit includes a switch configured to beelectrically coupled across the second converting unit. The secondconverting unit is configured to be coupled to an electric load. Also,the switching unit includes a controller electrically coupled to theswitch and configured to generate and feed a control signal having adetermined duty cycle to the switch to regulate an output DC voltageacross the electric load.

In accordance with another embodiment of the present invention, a methodfor protecting a wireless power transfer system is disclosed. The methodincludes converting, by a first converting unit, a first DC voltage ofan input power to a first AC voltage. Further, the method includesreceiving from the first converting unit and transmitting, by acontactless power transfer unit, the input power having the first ACvoltage. Also, the method includes converting, by a second convertingunit, the first AC voltage of the input power to a second DC voltage.Furthermore, the method includes transmitting the input power having thesecond DC voltage from the second converting unit to an electric load.In addition, the method includes regulating, by a switching unit, thesecond DC voltage across the electric load if the second DC voltageacross the electric load is greater than a voltage reference value.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram representation of a wireless power transfersystem having a switching unit in accordance with an embodiment of thepresent invention;

FIG. 2 is a schematic representation of a wireless power transfer systemin accordance with an embodiment of the present invention;

FIG. 3 is a schematic representation of a wireless power transfer systemin accordance with another embodiment of the present invention;

FIG. 4 is a flow chart illustrating a method for protecting a wirelesspower transfer system in accordance with an embodiment of the presentinvention;

FIG. 5 is a flow chart illustrating a method for decoupling and couplinga converting unit in a wireless power transfer system in accordance withan embodiment of the present invention; and

FIG. 6 is a flow chart illustrating a method for regulating an outputvoltage of a wireless power transfer system in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

As will be described in detail hereinafter, various embodiments of asystem and method for protecting a wireless power transfer system aredisclosed. Also, various embodiments of a system and method forregulating an output voltage of the wireless power transfer system aredisclosed. In particular, the system and method disclosed herein employa switching unit to protect one or more components in the wireless powertransfer system. More specifically, the switching unit decouples the oneor more components in the system if an output voltage of the wirelesspower transfer system increases to an undesirable value. Further, theswitching unit may be used to control or regulate the output voltage ofthe wireless power transfer system even if an electric load coupled tothe wireless power transfer system changes substantially.

FIG. 1 is a diagrammatical representation of a wireless power transfersystem 100 in accordance with an embodiment of the present invention.The wireless power transfer system 100 is used to transmit an electricalpower from a power source 102 to one or more electric loads 132 such as,batteries, light loads, mobile devices like cell phones, laptops, HVACsystems etc. Particularly, in an automobile industry, an electricvehicle or a hybrid vehicle includes one or more batteries that supplyelectrical power to drive the vehicle. Such batteries may beelectrically charged from the power source 102 via the wireless powertransfer system 100. In one embodiment, the wireless power transfersystem 100 may also be referred as a contactless power transfer system.

In the illustrated embodiment, the wireless power transfer system 100includes a first converting unit 104 (inverter), a control unit 106, acontactless power transfer unit 108, and a second converting unit 110(rectifier). The first converting unit 104 is electrically coupled tothe power source 102 and the control unit 106. The power source 102 isconfigured to supply an input power having a first DC voltage 112 to thefirst converting unit 104. In some embodiments, the input power may bein a range from about 100 W to about 6.6 kW. In one embodiment, thepower source 102 may be a part of the wireless power transfer system100. In another embodiment, the power source 102 may be positionedexternal to the wireless power transfer system 100.

The first converting unit 104 is configured to receive the input powerhaving the first DC voltage 112 from the power source 102. Further, thefirst converting unit 104 is configured to operate at a determinedswitching frequency to convert the first DC voltage 112 of the inputpower to a first AC voltage 114. Particularly, the control unit 106 maydetermine the switching frequency of the first converting unit 104 basedon the electric load 132 coupled to the wireless power transfer system100. In one example, the control unit 106 may include a digital circuitor a processor that performs one or more functions based on pre-storedinstructions or programs. Upon converting the first DC voltage 112 ofthe input power to the first AC voltage 114, the first converting unit104 is further configured to transmit the input power having the firstAC voltage 114 to the contactless power transfer unit 108.

The contactless power transfer unit 108 includes two or more coils or anarray of coils 116 that are magnetically coupled to each other. Thecoils 116 are used for wirelessly transmitting the input power havingthe first AC voltage 114 from the first converting unit 104 to thesecond converting unit 110. The details pertaining to transmitting thepower using the coils 116 are explained in greater detail below withreference to FIG. 2.

The second converting unit 110 is electrically coupled to thecontactless power transfer unit 108 via a switching unit 130. Uponreceiving the power having the first AC voltage 114 from the contactlesspower transfer unit 108, the second converting unit 110 is configured toconvert the power having the first AC voltage 114 to an output powerhaving a second DC voltage 118. Further, the second converting unit 110is configured to transmit the output power having the second DC voltage118 to the electric load 132. In one example, the output power may beused for charging the electric load including one or more batteries thatare coupled to the wireless power transfer system 100.

Additionally, the wireless power transfer system 100 includes a sensor120, a first transceiver 122, and a second transceiver 124 that togetherform a feedback loop 126. The sensor 120 is used to sense the second DCvoltage (output voltage) 118. The feedback loop 126 is used tocommunicate a voltage signal (V_(o)) 128 representative of the second DCvoltage 118 from the sensor 120 to the control unit 106 via the firsttransceiver 122 and the second transceiver 124. Further, the controlunit 106 may be used to adjust or change the switching frequency of thefirst converting unit 104 based on the received voltage signal (V_(o))128 to control or regulate the second DC voltage 118 across the electricload 132.

However, since the voltage signal (V_(o)) 128 is communicated using awireless communication path between the first transceiver 122 and thesecond transceiver 124, the control unit 106 may receive the voltagesignal (V_(o)) 128 after a certain time delay. In one embodiment, thedelay may be in a range from about 1 millisecond to about 5milliseconds.

The control unit 106 may not be able to timely control the second DCvoltage 118 across the electric load 132 due to the delay incommunicating the voltage signal (V_(o)) 128. As result, the second DCvoltage 118 may increase above a critical value, which in turn maydamage the second converting unit 110 and/or other components in thewireless power transfer system 100. The critical value may be a voltagevalue above which the components in the wireless power transfer system100 may be damaged. In one embodiment, the critical value may be in arange from about 400V to about 500V.

To overcome the issues related to increase of the second DC voltage 118above a critical value, the exemplary wireless power transfer system 100includes the switching unit 130 to protect the second converting unit110 from damage. Particularly, the switching unit 130 is electricallycoupled to the contactless power transfer unit 108 and the secondconverting unit 110. The switching unit 130 is configured to decouplethe second converting unit 110 from the contactless power transfer unit108 if the second DC voltage 118 is greater than a first threshold value(V_(o) Max). The first threshold value (V_(o) Max) may be less than thecritical value. In one embodiment, the first threshold value (V_(o) Max)may be in a range from about 350V to about 450V.

The input power is not transmitted to the second converting unit 110 orthe electric load 132 by decoupling the second converting unit 110 fromthe contactless power transfer unit 108. As a result, the second DCvoltage 118 across the electric load 132 may be reduced below the firstthreshold value (V_(o) Max). The switching unit 130 is configured toprevent the second DC voltage 118 from attaining a critical value, whichin turn protects the second converting unit 110 from damage. Theprotection of the second converting unit 110 is described in greaterdetail with reference to FIG. 2.

Furthermore, in one embodiment, the switching unit 130 may be used toregulate or control the second DC voltage 118 across the electric load132. If the second DC voltage 118 is greater than a voltage referencevalue (V_(o)ref), the switching unit 130 is configured to regulate orcontrol the second DC voltage 118 without decoupling the secondconverting unit 110 from the contactless power transfer unit 108. Theregulation of the second DC voltage 118 is described in greater detailwith reference to FIG. 3.

Referring to FIG. 2, a schematic representation of a wireless powertransfer system 200 in accordance with an embodiment of the presentinvention is depicted. The wireless power transfer system 200 is similarto the wireless power transfer system 100 of FIG. 1. The wireless powertransfer system 200 is used to transmit an input power from a powersource 202 to an electric load 232 such as one or more batteries in anelectric or hybrid vehicle.

The wireless power transfer system 200 includes a first converting unit204, a control unit 206, a contactless power transfer unit 208, a secondconverting unit 210, a switching unit 212, a first transceiver 214, anda second transceiver 216. It may be noted that the wireless powertransfer system 200 may include other components and may not be limitedto the components shown in FIG. 2.

In the illustrated embodiment, the first converting unit 204 iselectrically coupled to the power source 202 and configured to receivethe input power having a first DC voltage 218 from the power source 202.The first converting unit 204 includes a plurality of switches 220 anddiodes 222 that are electrically coupled between an input terminal andan output terminal of the first converting unit 204. In one example, theswitches 220 may include electronic switches, such as MOSFETs or IGBTs.The plurality of switches 220 and the diodes 222 are arranged to form aDC-AC converter.

The switches 220 are activated and deactivated based on a switchingfrequency of the first converting unit 204 to convert the first DCvoltage 218 of the input power to a first AC voltage 224. Particularly,the control unit 206 is configured to determine the switching frequencyof the first converting unit 204 based on the electric load 232 coupledto the wireless power transfer system 200. Further, the control unit 206is configured to send one or more gate signals 226 that arerepresentative of the switching frequency to the plurality of switches220 in the first converting unit 204 to convert the first DC voltage 218of the input power to the first AC voltage 224. The input power havingthe first AC voltage 224 is transmitted from the first converting unit204 to the contactless power transfer unit 208.

The contactless power transfer unit 208 is electrically coupled to thefirst converting unit 204 for receiving the input power having the firstAC voltage 224. The contactless power transfer unit 208 includes aprimary coil 228 and a secondary coil 230. The primary coil 228 iselectrically coupled to the first converting unit 204. In a similarmanner, the secondary coil 230 is electrically coupled to the secondconverting unit 210. The primary coil 228 and the secondary coil 230 aremagnetically coupled to each other.

In addition to the primary coil 228 and the secondary coil 230, thecontactless power transfer unit 208 includes a field focusing coil 234and a compensation coil 236. The field focusing coil 234 is positionedbetween the primary coil 228 and the secondary coil 230. The fieldfocusing coil 234 is magnetically coupled to the primary coil 228 andthe secondary coil 230. In a similar manner, the compensation coil 236is magnetically coupled to the secondary coil 230. It may be noted thatthe contactless power transfer unit 208 may include two or more coilsfor transferring the power from the first converting unit 204 to thesecond converting unit 210.

Further, the input power having the first AC voltage 224 from the firstconverting unit 204 is configured to excite the primary coil 228 and thefield focusing coil 234 simultaneously. The magnetic field generated bythe primary coil 228 is focused towards the secondary coil 230 via thefield focusing coil 234. The secondary coil 230 is configured to receivethe magnetic field and convert the magnetic field to the input powerhaving the first AC voltage 224. The power having the first AC voltage224 is then transmitted from the secondary coil 230 to the secondconverting unit 210. In one embodiment, the field focusing coil 234 iselectrically coupled to one or more resonators that are arranged in anarray which are excited by the input power simultaneously to enhance thecoupling between the primary coil 228 and the secondary coil 230. Thecompensation coil 236 is configured to match an impedance of thecontactless power transfer unit 208 with the second converting unit 210.

The second converting unit 210 is configured to convert the power havingthe first AC voltage 224 to an output power having a second DC voltage238. Particularly, the second converting unit 210 includes a pluralityof diodes, MOSFETs, or IGBTs 240 that are electrically coupled betweenan input terminal and an output terminal of the second converting unit210. The power having the second DC voltage 238 is transmitted to theelectric load 232. In one embodiment, the electric load 232 may bebatteries that are electrically charged by using the power received fromthe second converting unit 210. It may be noted that herein the terms“output voltage” and “second DC voltage” may be used interchangeably.

Additionally, the wireless power transfer system 200 includes a sensor244, a first transceiver 214, and a second transceiver 216 that togetherform a feedback loop 242. The feedback loop 242 is used forcommunicating load information and/or the second DC voltage informationto the control unit 206. More specifically, the sensor 244 iselectrically coupled to the output terminal of the second convertingunit 210 to determine the second DC voltage 238 across the electric load232. In one embodiment, the sensor 244 may be a voltage sensor. In suchan embodiment, the sensor 244 is configured to transmit a voltage signal(V_(o)) 246 that is representative of the determined second DC voltage238 to the first transceiver 214.

The first transceiver 214 includes an antenna 248 configured to transmitthe voltage signal (V_(o)) 246 towards an antenna 250 of the secondtransceiver 216. In one embodiment, the first transceiver 214 may bepositioned proximate to the electric load 232 and the second transceiver216 may be positioned proximate to the first converting unit 204 or thepower source 202. The second transceiver 216 is configured to receivethe voltage signal (V_(o)) 246 transmitted by the first transceiver 214.Further, the second transceiver 216 is configured to transmit thereceived voltage signal (V_(o)) 246 to the control unit 206.

The control unit 206 is configured to determine a change in the electricload 232 based on the voltage signal (V_(o)) 246 representative of thesecond DC voltage 238. In response to receiving the voltage signal(V_(o)) 246, the control unit 206 is configured to determine or adjustthe switching frequency of the first converting unit 204. Further, thecontrol unit 206 is configured to send gate signals 226 that arerepresentative of the switching frequency to the first converting unit204 to control the first AC voltage 224 of the first converting unit204, which in turn controls the second DC voltage 238 across theelectric load 232. In other words, the control unit 206 is configured tocontrol or regulate the second DC voltage 238 of the wireless powertransfer system 200 based on the voltage signal (V_(o)) 246 received viathe feedback loop 242.

Similar to the embodiment of FIG. 1, in order to overcome the issuesrelated to increase of the second DC voltage 2388 above a criticalvalue, the exemplary wireless power transfer system 200 includes theswitching unit 212 configured to protect the second converting unit 210from damage. The switching unit 212 includes a switch 252 and acontroller 254. The controller 254 is electrically coupled to the switch252 and the sensor 244.

In the illustrated embodiment, the switch 252 is electrically coupledacross the second converting unit 210. The switch 252 is activated ifthe switch 252 receives a first control signal from the controller 254.Specifically, the switch 252 is activated or closed to short-circuit thesecondary coil 230, which in turn decouples the second converting unit210 from the secondary coil 230. Similarly, the switch 252 may bedeactivated if the switch 252 receives a second control signal from thecontroller 254. Specifically, the switch 252 is deactivated or opened tocouple the secondary coil 230 to the second converting unit 210.

The controller 254 includes a first comparator 256, a second comparator258, and a flip-flop unit 260. The first comparator 256 and the secondcomparator 258 is electrically coupled to an input terminal of theflip-flop unit 260. An input terminal of the controller 254 is coupledto the first comparator 256 and the second comparator 258. An outputterminal of the controller 254 is coupled to the flip-flop unit 260.

The controller 254 is configured to receive the voltage signal (V_(o))246 that is representative of the second DC voltage 238 from the sensor244. Further, the received voltage signal (V_(o)) 246 is transmitted tothe first comparator 256 and the second comparator 258. The firstcomparator 256 is configured to compare the second DC voltage 238 with afirst threshold value (V_(o) Max). If the second DC voltage 238 isgreater than the first threshold value (V_(o) Max), the first comparator256 is configured to trigger the flip-flop unit 260 to generate thefirst control signal at the output terminal of the controller 254.

Similarly, the second comparator 258 is configured to receive thevoltage signal (V_(o)) 246 that is representative of the second DCvoltage 238. Further, the second comparator 258 is configured to comparethe received second DC voltage 238 with a second threshold value (V_(o)Min). It should be noted herein that the second threshold value (V_(o)Min) is less than the first threshold value (V_(o) Max). If the secondDC voltage 238 is less than the second threshold value (V_(o) Min), thesecond comparator 258 is configured to trigger the flip-flop unit 260 togenerate the second control signal at the output terminal of thecontroller 254.

During normal operation of the wireless power transfer system 200, theswitch 252 is deactivated to couple the second converting unit 210 tothe contactless power transfer unit 208. The second DC voltage 238across the electric load 232 is controlled or regulated by the controlunit 206 based on the voltage signal (V_(o)) 246 received from thesensor 244 via the first transceiver 214 and the second transceiver 216.The controller 254 does not activate or close the switch 252 if thesecond DC voltage 238 is less than the first threshold value (V_(o)Max).

In certain circumstances, if the full load 232 or a portion of the load232 is disconnected or decoupled suddenly from the second convertingunit 210, the second DC voltage 238 across the load 232 may increaseabove the first threshold value (VoMax). The sensor 244 determines andsend the voltage signal (V_(o)) 246 that is representative of thissecond DC voltage 238 to the controller 254 and the first transceiver214. At the controller 254, the first comparator 256 compares the secondDC voltage 238 with the first threshold value (V_(o) Max). If the secondDC voltage 238 is greater than the first threshold value (V_(o) Max),the first comparator 256 triggers the flip-flop unit 260 to generate thefirst control signal which is transmitted to the switch 252 todeactivate the switch 252. As a result, the second converting unit 210is decoupled from the contactless power transfer unit 208.

Concurrently, the first control signal is transmitted from thecontroller 254 to the first transceiver 214. Further, the firsttransceiver 214 transmits the voltage signal (V_(o)) 246 received fromthe sensor 244 and the first control signal received from the controller254 to the second transceiver 216. The voltage signal (V_(o)) 246 andthe first control signal are further transmitted to the control unit206.

Upon receiving the voltage signal (V_(o)) 246 and the first controlsignal, the control unit 206 determines that the switch 252 is activatedin the wireless power transfer system 200 based on the received firstcontrol signal. As a result, the control unit 206 deactivates the firstconverting unit 204. In one embodiment, the control unit 204 sends thegate signals 226 to the switches 220 in the first power converting unit204 to deactivate or open the switches 220. As a result, the firstconverting unit 204 is deactivated or suspended from transmitting thepower to the contactless power transfer unit 208 and the secondconverting unit 210.

Furthermore, after a predetermined time period, the control unit 206sends a reset signal 262 to the second transceiver 216, which is furthertransmitted to the first transceiver 214. The first transceiver 216sends the reset signal 262 to the flip-lop unit 260 in the controller254. In response to receiving the reset signal 262, the flip-flip unit260 resets and generates the second control signal at the outputterminal of the controller 254. The generated second control signal istransmitted to the switch 252 to deactivate or open the switch 252 sothat the second converting unit 210 is coupled to the contactless powertransfer unit 208 to permit the second converting unit 210 to continuesupplying power having the second DC voltage 238 to the electric load232.

Concurrently, the generated second control signal at the controller 254is transmitted to the first transceiver 214. In addition to the secondcontrol signal, the first transceiver 214 receives the voltage signal(V_(o)) 246 representative of the second DC voltage 238 across the load232. Further, the first transceiver 214 transmits the voltage signal(V_(o)) 246 and the second control signal to the second transceiver 216,which is further transmitted to the control unit 206.

Upon receiving the voltage signal (V_(o)) 246 and the second controlsignal from the second transceiver 216, the control unit 206 determineswhether the second DC voltage 238 is less than or equal to the firstthreshold value (V_(o) Max). If the second DC voltage 238 is less thanor equal to the first threshold value (V_(o) Max), the control unit 206sends the gate signals 226 to the switches 220 in the first convertingunit 204 to activate the first converting unit 204. Further, the controlunit 206 adjusts or changes the switching frequency of the firstconverting unit 204 based on the second DC voltage 238 across theelectric load 232. In one embodiment, the control unit 206 adjusts orchanges the switching frequency of the first converting unit 204 toregulate or control the second DC voltage 238 across the electric load232. If the second DC voltage 238 is greater than the first thresholdvalue (V_(o) Max), the control unit 206 waits for the predetermined timeperiod to send another reset signal to the controller 254. If the secondDC voltage 238 continues to be greater than the first threshold value(V_(o) Max) after transmitting the reset signal for a predeterminednumber of times, the control unit 206 deactivates the system 200.

Accordingly, by employing the switching unit 212 and the control unit206, the second DC voltage 238 is prevented from increasing above thecritical value. As a result, the second converting unit 210 is protectedfrom damage even if the electric load 232 gets disconnected or decoupledfrom the wireless power transfer system 200.

Referring to FIG. 3, a schematic representation of a wireless powertransfer system 300 in accordance with another embodiment of the presentinvention. The wireless power transfer system 300 is similar to thewireless power transfer system 200 of FIG. 2 except that a controller302 in the switching unit 212 is configured to regulate or control thesecond DC voltage 238 (output voltage) of a second converting unit 210.

During operation, if the electric load 232 gets disconnected from thewireless power system 300, the second DC voltage 238 across the load 232may increase above a voltage reference value (V_(o)ref). It is requiredto control or regulate the second DC voltage 238 so that the second DCvoltage 238 is not increased above a critical value. In one example, thevoltage reference value (V_(o)ref) is less than the critical value.

The sensor 244 determines the second DC voltage 238 across the electricload 232. Further, the sensor 244 transmits a voltage signal (V_(o)) 246representative of the second DC voltage 238 to the controller 302. Atthe controller 302, the second DC voltage 238 is compared with thevoltage reference value (V_(o)ref). If the second DC voltage 238 isgreater than the voltage reference value (V_(o)ref), the controller 302generates a control signal 304 having a determined duty cycle to controlthe switch 252. In one embodiment, the controller 302 may determine orselect the duty cycle using a look-up table. For example, if the secondDC voltage 238 is 90 volts, a duty cycle of 0.75 corresponding to 90volts is selected from the look-up table. In another example, if thesecond DC voltage 238 is 170 volts, a duty cycle of 0.5 corresponding to170 volts is selected from the look-up table. In yet another example, ifthe second DC voltage 238 is 250 volts, a duty cycle of 0.25corresponding to 250 volts is selected from the look-up table.

The controller 302 transmits the control signal 304 having thedetermined duty cycle to the switch 252 to regulate or control thesecond DC voltage 238 across the load 232. Particularly, the controlsignal 304 includes switching pulses having the determined duty cycle.The switching pulses are transmitted to the switch 252 to regulate orcontrol the second DC voltage 238 across the load 232.

Concurrently, the voltage signal (V_(o)) 246 is transmitted from thesensor 244 to the first transceiver 214. Further, the first transceiver214 transmits the voltage signal (V_(o)) 246 to the second transceiver216, which in turn is transmitted to the control unit 206.

At the control unit 206, gate signals 226 are generated based on thesecond DC voltage 238. Further, the control unit 206 transmit the gatesignals 226 to the switches 220 in the first converting unit 204 toadjust or change the switching frequency of the first converting unit204. As a result, the first AC voltage 224 from the first convertingunit 204 is regulated, which in turn controls or regulates the second DCvoltage 238 across the load 232. However, the regulation of the secondDC voltage 238, using the control unit 206, occurs after the regulationof the second DC voltage, using the controller 302. Hence, thecontroller 302 may perform faster regulation of the second DC voltage238 compared to the regulation of the second DC voltage 238 by thecontrol unit 206.

Accordingly, the second DC voltage 238 across the load 232 is regulatedor controlled by employing the switching unit 212 before the second DCvoltage 238 reaches the critical value. As a result, the secondconverting unit 210 is prevented from damage even if the electric load232 is disconnected from the wireless power transfer system 300.

Referring to FIG. 4, a flow chart illustrating a method 400 forprotecting the wireless power transfer system in accordance with aspectsof the present invention is depicted. The method 400 is described withreference to the components of FIGS. 1 and 2. At step 402, a first DCvoltage of an input power is converted to a first AC voltage. A firstconverting unit is coupled to a power source for receiving the inputpower having the first DC voltage. The first converting unit is operatedat a determined switching frequency to convert the first DC voltage ofthe input power to the first AC voltage.

Subsequently, at step 404, the method includes receiving andtransmitting the input power having the first AC voltage. Particularly,a contactless power transfer unit is electrically coupled to the firstconverting unit to receive the input power having the first AC voltage.The contactless power transfer unit transmits the input power having thefirst AC voltage to a second converting unit. Furthermore, at step 406,the first AC voltage of the input power is converted to a second DCvoltage. A second converting unit is electrically coupled to thecontactless power transfer unit to receive the input power having thefirst AC voltage. Further, the second converting unit converts the firstAC voltage of the input power to the second DC voltage. At step 408, theinput power having the second DC voltage is transmitted from the secondconverting unit to an electric load. In one embodiment, the electricload may be one or more batteries that are electrically charged usingthe input power having the second DC voltage received from the secondconverting unit.

At step 410, the second converting unit is decoupled from thecontactless power transfer unit if the second DC voltage across theelectric load is greater than a first threshold value (V_(o) Max).Specifically, a switching unit is used to decouple the second convertingunit from the contactless power transfer unit. As a result, the secondDC voltage across the electric load is reduced below the first thresholdvalue (V_(o) Max), thereby protecting the second converting unit fromdamage due to over voltage. Furthermore, if the determined second DCvoltage is less than a second threshold value (V_(o) Min), the switchingunit couples the second converting unit to the contactless powertransfer unit to continue supplying power having the second DC voltageto the electric load.

Referring to FIG. 5, a flow chart illustration a method for decouplingand coupling a second converting unit in a wireless power transfersystem in accordance with an embodiment of the present invention isdepicted. Specifically, the method 500 includes steps involved in thestep 410 of FIG. 4. At step 502, a voltage signal (V_(o)) representativeof a second DC voltage across an electric load is transmitted by asensor. More specifically, the sensor transmits the voltage signal(V_(o)) to a controller. Further, the sensor transmits the voltagesignal (V_(o)) to a control unit via a first transceiver and a secondtransceiver.

Subsequently, at step 504, the controller determines whether the voltagesignal (V_(o)) representative of the second DC voltage is greater than afirst threshold value (V_(o) Max). If the voltage signal (V_(o))representative of the second DC voltage is greater than the firstthreshold value (V_(o) Max), the controller transmits a first controlsignal to a switch to activate or close the switch as depicted in step506. As a result, the second converting unit is decoupled from thecontactless power transfer unit and thereby the second DC voltage acrossthe load is reduced below the first threshold value (V_(o) Max). Morespecifically, the second DC voltage is prevented from reaching acritical value that is greater than the first threshold value (V_(o)Max). The critical value may be a voltage value above which the secondconverting unit may be damaged. Concurrently, the controller sends afirst control signal to the control unit via the first transceiver andthe second transceiver.

Furthermore, at step 508, the controller determines whether the voltagesignal (V_(o)) representative of the second DC voltage is less than asecond threshold value (V_(o) Min). If the voltage signal (V_(o))representative of the second DC voltage is less than the secondthreshold value (V_(o) Min), the controller sends a second controlsignal to the switch to deactivate or open the switch as depicted instep 510. As a result, the second converting unit is coupled to thecontactless power transfer unit to receive and supply the power to theelectric load.

At step 512, the control unit receives the voltage signal (V_(o)) andthe first control signal. The control unit receives the voltage signal(V_(o)) from the sensor via the first transceiver and the secondtransceiver. The control unit receives the first control signal from thecontroller via the first transceiver and the second transceiver.

Subsequently, at step 514, the control unit deactivates the firstconverting unit if the first control signal is received from thecontroller. The first converting unit is deactivated to prevent thesupply of input power to the second converting unit. Furthermore, atstep 516, the control unit, transmits a reset signal to the controllervia the first transceiver and the second transceiver after apredetermined time period. In response to receiving the reset signal,the controller generates the second control signal. Further, thecontroller sends the second control signal to the switch to deactivateor open the switch. As a result, the second converting unit is coupledto the contactless power transfer unit to receive and supply the powerto the electric load at step 508.

Concurrently, at step 518, the controller transmits the second controlsignal to the control unit via the first transceiver and the secondtransceiver. Further, the sensor transmits the voltage signal (V_(o)) tothe control unit via the first transceiver and the second transceiver.Subsequently, at step 520, the control unit determines whether thevoltage signal (V_(o)) representative of the second DC voltage is lessthan or equal to the first threshold value (V_(o) Max). If the second DCvoltage is less than or equal to the first threshold value (V_(o) Max),the control unit transmits gate signals to activate the first convertingunit. As a result, the input power is supplied to the second convertingunit via the contactless power transfer unit. Further, the electric loadreceives the power having the second DC voltage from the secondconverting unit. As a result, one or more components in the wirelesspower transfer unit are protected from increase in the second DC voltageacross the load.

Referring to FIG. 6, a flow chart illustrating a method for regulatingan output voltage of a wireless power transfer system in accordance withan embodiment of the present invention is depicted. At step 602, a firstDC voltage of an input power is converted to a first AC voltage.Specifically, a first converting unit is coupled to a power source forreceiving the input power having the first DC voltage. Further, thefirst converting unit is operated at a determined switching frequency toconvert the first DC voltage of the input power to the first AC voltage.

Subsequently, at step 604, the method includes receiving andtransmitting the input power having the first AC voltage. Particularly,a contactless power transfer unit is electrically coupled to the firstconverting unit to receive the input power having the first AC voltage.Further, the contactless power transfer unit transmits the input powerhaving the first AC voltage to a second converting unit.

Furthermore, at step 606, the first AC voltage of the input power isconverted to a second DC voltage. The second converting unit iselectrically coupled to the contactless power transfer unit to receivethe input power having the first AC voltage. Further, the secondconverting unit converts the first AC voltage of the input power to thesecond DC voltage. At step 608, the input power having the second DCvoltage is transmitted from the second converting unit to an electricload. In one embodiment, the electric load may be one or more batteriesthat are electrically charged by the input power having the second DCvoltage received from the second converting unit.

In addition, at step 610, the second DC voltage across the electric loadis regulated if the second DC voltage across the electric load isgreater than a voltage reference value (V_(o)ref). A switching unit iselectrically coupled to the second converting unit and configured toregulate the second DC voltage across the electric load. Particularly, asensor coupled to an output terminal of the second converting unit isused to determine the second DC voltage across the electric load.Further, a controller which is coupled to the sensor, is used togenerate a control signal having a determined duty cycle based on thesecond DC voltage. More specifically, the controller compares the secondDC voltage with a voltage reference value (V_(o)ref). If the second DCvoltage is greater than the voltage reference value (V_(o)ref), thecontroller determines or selects a duty cycle corresponding to thesecond DC voltage. Further, the controller generates the control signalhaving the selected or determined duty cycle. Thereafter, the controllerfeeds the control signal having the determined duty cycle to the switchto regulate the second DC voltage across the electric load to protectthe second converting from damage due to over voltage.

In accordance with the exemplary embodiments discussed herein, theexemplary system and method facilitate to protect one or more componentsin the wireless power transfer system when the load is disconnected.Further, the exemplary system and method facilitate to control orregulate the output voltage when the load is disconnected. As a result,one or more components in the system are protected without decouplingthe components from each other in the system.

While only certain features of the present disclosure have beenillustrated and described herein, many modifications and changes willoccur to those skilled in the art. It is, therefore, to be understoodthat the appended claims are intended to cover all such modificationsand changes as fall within the true spirit of the present disclosure.

1. A wireless power transfer system comprising: a first converting unitconfigured to convert a first DC voltage of an input power to a first ACvoltage; a contactless power transfer unit communicatively coupled tothe first converting unit and configured to receive the input powerhaving the first AC voltage from the first converting unit and transmitthe input power; a second converting unit communicatively coupled to thecontactless power transfer unit and configured to receive the inputpower from the contactless power transfer unit and convert the first ACvoltage of the input power to a second DC voltage, wherein the inputpower having the second DC voltage is transmitted to an electric load;and a switching unit coupled to the contactless power transfer unit andthe second converting unit and configured to regulate the second DCvoltage across the electric load if the second DC voltage across theelectric load is greater than a voltage reference value.
 2. The wirelesspower transfer system of claim 1, wherein the switching unit comprises:a switch electrically coupled across the second converting unit; asensor electrically coupled to the electric load and configured todetermine the second DC voltage across the electric load; and acontroller electrically coupled to the sensor and the switch andconfigured to determine a duty cycle of a control signal configured tocontrol the switch, based on the determined second DC voltage.
 3. Thewireless power transfer system of claim 2, wherein the controller isconfigured to generate and feed the control signal having the determinedduty cycle to the switch to regulate the second DC voltage across theelectric load.
 4. The wireless power transfer system of claim 2, furthercomprising a first transceiver electrically coupled to the sensor andconfigured to receive and transmit a voltage signal representative ofthe second DC voltage across the electric load.
 5. The wireless powertransfer system of claim 4, further comprising a second transceivercommunicatively coupled to the first transceiver and configured toreceive the voltage signal from the first transceiver.
 6. The wirelesspower transfer system of claim 5, further comprising a control unitelectrically coupled to the second transceiver and the first convertingunit and configured to adjust a switching frequency of the firstconverting unit based on the voltage signal representative of the secondDC voltage across the electric load.
 7. The wireless power transfersystem of claim 6, wherein the control unit is configured to adjust theswitching frequency of the first converting unit to regulate the secondDC voltage across the electric load.
 8. The wireless power transfersystem of claim 7, wherein the control unit is configured to regulatethe second DC voltage across the electric load after the controllerregulates the second DC voltage across the electric load.
 9. Thewireless power transfer system of claim 1, further comprising a powersource configured to provide the input power to the first convertingunit.
 10. A switching unit for protecting a wireless power transfersystem comprising a first converting unit, a contactless power transferunit, and a second converting unit, the switching unit comprising: aswitch configured to be electrically coupled across the secondconverting unit, wherein the second converting unit is configured to becoupled to an electric load; and a controller electrically coupled tothe switch and configured to generate and feed a control signal having adetermined duty cycle to the switch to regulate an output DC voltageacross the electric load.
 11. The switching unit of claim 10, whereinthe controller is configured to generate and feed the control signal tothe switch if the output DC voltage across the electric load is greaterthan a voltage reference value.
 12. The switching unit of claim 10,further comprising a sensor electrically coupled to the controller andthe electric load and configured to determine the output DC voltageacross the electric load.
 13. The switching unit of claim 12, whereinthe controller is configured to determine the duty cycle of the controlsignal based on the determined output DC voltage across the electricload.
 14. A method for protecting a wireless power transfer system, themethod comprising: converting, by a first converting unit, a first DCvoltage of an input power to a first AC voltage; receiving from thefirst converting unit and transmitting, by a contactless power transferunit, the input power having the first AC voltage; and converting, by asecond converting unit, the first AC voltage of the input power to asecond DC voltage, transmitting the input power having the second DCvoltage from the second converting unit to an electric load; andregulating, by a switching unit, the second DC voltage across theelectric load if the second DC voltage across the electric load isgreater than a voltage reference value.
 15. The method of claim 14,wherein regulating the second DC voltage comprises: determining, by asensor, the second DC voltage across the electric load; determining, bya controller, a duty cycle of a control signal configured to control aswitch, based on the determined second DC voltage; generating andfeeding, by the controller, the control signal having the determinedduty cycle to the switch to regulate the second DC voltage across theelectric load.
 16. The method of claim 15, further comprising:transmitting from the sensor, by a first transceiver, a voltage signalrepresentative of the second DC voltage across the electric load; andreceiving the voltage signal by a second transceiver from the firsttransceiver.
 17. The method of claim 16, further comprising adjusting,by a control unit, a switching frequency of the first converting unitbased on the voltage signal to regulate the second DC voltage across theelectric load.
 18. The method of claim 17, wherein the switchingfrequency of the first converting unit is adjusted after feeding thecontrol signal to the switch.
 19. The method of 17, further comprisingregulating the second DC voltage across the electric load by the controlunit after regulating the second DC voltage across the electric load bythe controller.